It is understood that there are driver assistance systems which support the driver in keeping to a selected traffic lane. For this purpose, the driver assistance system includes assistance functions such as LDW (lane departure warning) and/or LKS (lane keeping support). Assistance function LDW warns the driver of leaving the traffic lane by generating optical and/or acoustic and/or haptic signals. Assistance function LKS actively intervenes in on-board systems of the vehicle, such as the steering system, for example, and/or the braking system or an ESP system, in order to keep a vehicle deviating from the traffic lane in the traffic lane. For this purpose, the driver assistance system includes a sensor system including in particular at least one video sensor for detecting traffic lane markings or the like.
German patent document DE 101 37 292 A1 discusses a method for operating a driver assistance system of a vehicle, particularly of a motor vehicle, having a servo-supported steering system. This method is characterized by the following steps:                acquiring or estimating surroundings data, which may be of a current traffic situation,        acquiring or estimating what may be current motion data of the vehicle,        comparing the acquired or estimated surroundings data to the motion data of the vehicle,        modifying the support of a steering handle in accordance with the comparison.        
By way of restrictions, e.g. in the detecting range of sensors used in the driver assistance system or in the validity of model assumptions made in the design of the driver assistance system, system boundaries are defined beyond which the driver himself must again assume full control over guiding the vehicle. When a predefined system boundary is reached, for example by losing the traffic lane or its marking, exceeding a maximum value of lateral acceleration or the like, the assistance function provided until this point in time by the driver assistance system is deactivated.
In a driver assistance system having an LKS function, the guidance torque applied by the driver assistance system on the steering wheel is then reduced for example. The driver himself must then completely take over again the lateral guidance of the vehicle. Because the mentioned system boundaries of a driver assistance system are exclusively technically motivated, they are often not intelligible or comprehensible for a driver since they do not coincide with his own perception. This results in uncertainty on the part of the driver and in a lack of acceptance of the driver assistance system.